Cell migration is inherently a physical process, guided by extracellular and intracellular chemical gradients, physical forces and structural architectures. In this proposal, we are answering the question: How do the physical components of the tumor microenvironment contribute to metastatic migration? Our overarching hypothesis is that specific chemical gradients created by cells within the 3D tumor microenvironment and changes in extracellular matrix (ECM) enable and enhance cell migration during metastasis. We will employ concepts and tools from the physical sciences to dissect the complex chemical and physical microenvironmental factors guiding cell migration during metastasis. To do this, we propose to use well-defined model tissue constructs where the cellular environment is tightly controlled to describe and measure a set of physical parameters that define the invasive behavior of tumor cells; the motility of a cell (Diffusivity, D), chemotactic response (Persistence, P), and the propulsive force (F). These measurements will be made of well-characterized cell lines and breast cancer patient-derived primary tumor cells as a function of the chemical and mechanical microenvironments, with and without targeted therapeutics. These parameters will be correlated with disease stage, clinical classification of invasiveness and time to recurrence and will in turn be fed back to our quantitative models to inform and refine them. Measurement of these parameters will lead to a more complete description of the physical regulators of metastatic migration, and the identification of novel targets for therapeutics which disrupt metastatic cell migration. This proposal will answer the following questions: Does cellular physical force generation correlate with the metastatic tumor cell potential? Does the chemical microenvironment created by surrounding immune cells and vascular cells control the metastatic migratory phenotype? Does the increased mechanical stiffness of solid tumor ECM enable the migratory phenotype via increases in cell force? What is the role of microtubule dynamics and selected tubulin posttranslational modifications in the process of cell migration in response to distinct ECM chemomechanical cues? How do microtubule-targeting chemotherapeutic drugs modulate these behaviors and how is individual patient sensitivity to therapy affected by the interplay between ECM chemical gradients and mechanical forces and resident tumor cells? This work represents a paradigm shift over traditional 2D cell migration studies as it underscores the need to systematically de-convolve the complex 3D chemical and mechanical microenvironmental conditions affecting tumor cell migration. With this proposal we are integrating novel, quantitative methodologies from the discipline of physical sciences to systematically and robustly answer fundamental and complex questions in cancer biology and molecular oncology. Our work promises to understand the role of microenvironment in metastasis and has the potential of translating this knowledge into actual clinical gains.